Part 2

In the small room shown at the south side of the laboratory is placed a powerful electric fan which draws the air from above the floor of the calorimeter laboratory, draws it over brine coils, and sends it out into a large duct suspended on the ceiling of the laboratory. This duct has a number of openings, each of which can be controlled by a valve, and an unlimited supply of cold air can be directed to any portion of the calorimeter room at will. To provide for more continuous operation and for more exact temperature control, a thermostat has been placed in the duct and is so constructed as to operate some reheater coils beneath the brine-coils in the refrigerating room. This thermostat is set at 60 deg. F., and when the temperature of the air in the duct falls below this point, the reheater system is automatically opened or closed. The thermostat can be set at any point desired. Up to the present time it has been unnecessary to utilize this special appliance, as the control by hand regulation has been most satisfactory.

Two vertical sections through the refrigerating coils are shown in fig. 6. Section A-B shows the entrance near the floor of the calorimeter room. The air is drawn down over the coils, passes through the blower, and is forced back again to the top of the calorimeter room into the large duct. If outdoor air is desired, a special duct can be connected with the system so as to furnish outdoor air to the chamber. This has not as yet been used. Section C-D shows the fan and gives a section through the reheater. The brine coils, 400 meters long, are in triplicate. If one set becomes covered with moisture and is somewhat inefficient, this can be shut off and the other two used. When the frozen moisture melts and drops off, the single coil can be used again. It has been found that the system so installed is most readily controlled.

The degree of refrigeration is varied in two ways: (1) the area of brine coils can be increased or decreased by using one, two, or all three of the coils; or (2) the amount of air passing over the cooling pipes may be varied by changing the speed of the blower. In practice substantially all of the regulation is effected by varying the position of the controlling lever on the regulating rheostat. The apparatus functionates perfectly and the calorimeter room can be held at 20 deg. C. day in and day out, whether the temperature outdoors is 40 deg. below or 100 deg. above 0 deg. F.

It can be seen, also, that this system provides a very satisfactory regulation of the humidity, for as the air passes over the brine coils the moisture is in large part frozen out. As yet, no hygrometric study has been made of the air conditions over a long period, but the apparatus is sufficiently efficient to insure thorough electrical insulation and absence of leakage in the intricate electrical connections on the calorimeters.

The calorimeters employ the thermo-electric element with its low potential and a D'Arsonval galvanometer of high sensibility, and in close proximity it is necessary to use the 110-volt current for heating, consequently the highest degree of insulation is necessary to prevent disturbing leakage of current.

The respiration calorimeter laboratory is so large, the number of assistants in the room at any time is (relatively speaking) so small, seldom exceeding ten, and the humidity and temperature are so very thoroughly controlled, that as yet it has been entirely unnecessary to utilize even the relatively small amount of indirect ventilation provided in the original plans.

During the greater part of the winter it is necessary to use only one of the thermostats and the radiators connected with the other can be shut off, since each radiator can be independently closed by the valves on the steam supply and return which go through the floor to the basement. The temperature control of this room is therefore very satisfactory and economical.

It is not necessary here to go into the advantages of temperature control of the working rooms during the summer months. Every one seems to be thoroughly convinced that it is necessary to heat rooms in the winter, but our experience thus far has shown that it is no less important to cool the laboratory and control the temperature and moisture during the summer months, as by this means both the efficiency and endurance of the assistants, to say nothing of the accuracy of the scientific measurements, are very greatly increased. Arduous scientific observations that would be wholly impossible in a room without temperature control can be carried on in this room during the warmest weather.

FOOTNOTES:

[4] As this report goes to press, this calorimeter is well on the way to completion.

THE CALORIMETER.

In describing this apparatus, for the sake of clearness, the calorimetric features will be considered before the appliances for the determination of the respiratory products.

FUNDAMENTAL PRINCIPLES OF THE APPARATUS.

The measurements of heat eliminated by man, as made by this apparatus, are based upon the fact that the subject is inclosed in a heat-proof chamber through which a current of cold water is constantly passing. The amount of water, the flow of which, for the sake of accuracy, is kept at a constant rate, is carefully weighed. The temperatures of the water entering and leaving the chamber are accurately recorded at frequent intervals. The walls of the chamber are held adiabatic, thus preventing a gain or loss of heat by arbitrarily heating or cooling the outer metal walls, and the withdrawal of heat by the water-current is so controlled, by varying the temperature of the ingoing water, that the heat brought away from the calorimeter is exactly equal in amount to the heat eliminated by radiation and conduction by the subject, thus maintaining a constant temperature inside of the chamber. The latent heat of the water vaporized is determined by measuring directly the water vapor in the ventilating air-current.

In the construction of the new calorimeters a further and fundamental change in construction has been made in that all the thermal junctions, heating wires, and cooling pipes have been attached directly to the zinc wall of the calorimeter, leaving the outer insulating panels free from incumbrances, so that they can be removed readily and practically all parts inspected whenever desired without necessitating complete dismantling of the apparatus. This arrangement is possible except in those instances where connections pass clear through from the interior of the chamber to the outside, namely, the food-aperture, air-pipes, water-pipes, electrical connections, and tubes for connections with pneumograph and stethoscope; but the apparatus is so arranged as to have all of these openings in one part of the calorimeter. It is possible, therefore, to remove all of the outer sections of the calorimeter with the exception of panels on the east side.

This fundamental change in construction has proven highly advantageous. It does away with the necessity of rolling the calorimeter out of its protecting insulating house and minimizes the delay and expense incidental to repairs or modifications. As the calorimeter is now constructed, it is possible to get at all parts of it from the outside, with the exception of one small fixed panel through which the above connections are passed. This panel, however, is made as narrow as possible, so that practically all changes can be made by taking out the adjacent panels.

THE CALORIMETER CHAMBER.

The respiration chamber used in Middletown, Connecticut, was designed to permit of the greatest latitude in the nature of the experiments to be made with it. As a result, it was found at the end of a number of years of experimenting that this particular size of chamber was somewhat too small for the most satisfactory experiments during muscular work and, on the other hand, somewhat too large for the best results during so-called rest experiments. In the earlier experiments, where no attempt was made to determine the consumption of oxygen, these disadvantages were not so apparent, as carbon dioxide could be determined with very great accuracy; but with the attempts to measure the oxygen it was found that the large volume of residual air inside the chamber, amounting to some 4,500 liters, made possible very considerable errors in this determination, for, obviously, the subject could draw upon the oxygen residual in the air of the chamber, nearly 1,000 liters, as well as upon the oxygen furnished from outside sources. The result was that a very careful analysis of the residual air must be made frequently in order to insure that the increase or decrease in the amount of oxygen residual in the air of the chamber was known accurately at the end of each period. Analysis of this large volume of air could be made with considerable accuracy, but in order to calculate the exact total of oxygen residual in the air it was necessary to know the total volume of air inside the chamber under standard conditions. This necessitated, therefore, a careful measurement of temperature and pressure, and while the barometric pressure could be measured with a high degree of accuracy, it was found to be very difficult to determine exactly the average temperature of so large a mass of air. The difficulties attending this measurement and experiments upon this point are discussed in detail elsewhere.[5] Consequently, as a result of this experience, in planning the calorimeters for the Nutrition Laboratory it was decided to design them for special types of experiments. The first calorimeter to be constructed was one which would have general use in experiments during rest and, indeed, during experiments with the subject sitting quietly in the chair.

It may well be asked why the first calorimeter was not constructed of such a type as to permit the subject assuming a position on a couch or sofa, such as is used by Zuntz and his collaborators in their research on the respiratory exchange, or the position of complete muscular rest introduced by Johansson and his associates. While the body positions maintained by Zuntz and Johansson may be the best positions for experiments of short duration, it was found, as a result of a large number of experiments, that subjects could be more comfortable and quiet for periods of from 6 to 8 hours by sitting, somewhat inclined, in a comfortable arm-chair, provided with a foot-rest. With this in mind the first calorimeter was constructed so as to hold an arm-chair with a foot-rest so adjusted that the air-space between the body of the subject and the walls of the chamber could be cut down to the minimum and thus increase the accuracy of the determination of oxygen. That the volume has been very materially reduced may be seen from the fact that the total volume of the first calorimeter to be described is less than 1,400 liters, or about one-third that of the Middletown apparatus.

GENERAL CONSTRUCTION.

A horizontal cross-section of the apparatus is shown in fig. 7, and a vertical cross-section facing the front is given in fig. 8. Other details of structural steel are seen in fig. 9.

In constructing the new chambers, the earlier wood construction, with its tendency to warp and its general non-rigidity, was avoided by the use of structural steel, and hence in this calorimeter no use whatever is made of wood other than the wood of the chair.

To avoid temperature fluctuations due to possible local stratification of the air in the laboratory, the calorimeter is constructed so as to be practically suspended in the air, there being a large air-space of some 76 centimeters between the lowest point of the calorimeter and the floor, and the top of the calorimeter is some 212 centimeters below the ceiling of the room. Four upright structural-steel channels (4-inch) were bolted through the floor, so as to secure great rigidity, and were tied together at the top with structural steel. As a solid base for the calorimeter chamber two 3-inch channels were placed parallel to each other 70 centimeters from the floor, joined to these uprights. Upon these two 3-inch channels the calorimeter proper was constructed. The steel used for the most part in the skeleton of the apparatus is standard 2-1/2-inch channel. This steel frame and its support are shown in fig. 10, before any of the copper lining was put into position. The main 4-inch channels upon which the calorimeter is supported, the tie-rods and turn-buckles anchoring the framework to the ceiling, the I-beam construction at the top upon which is subsequently installed the large balance for weighing the man, the series of small channels set on edge upon which the asbestos floor is laid, and the upright row of channel ribs are all clearly shown.

A photograph taken subsequently, showing the inner copper lining in position, is given in fig. 11.

The floor of the chamber is supported by 7 pieces of 2-1/2-inch channel (N, N, N, fig. 8), laid on top and bolted to the two 3-inch channels (M, fig. 8). On top of these is placed a sheet of so-called asbestos lumber (J', fig. 8) 9.5 millimeters thick, cut to fit exactly the bottom of the chamber. Upright 2-1/2-inch channels (H, fig. 8) are bolted to the two outside channels on the bottom and to the ends of three of the long channels between in such a manner as to form the skeleton of the walls. The upper ends of these channels are fastened together by pieces of piping (P, P, P, fig. 8) with lock-nuts on either side, thus holding the whole framework in position.

The I-beams and channels used to tie the four upright channels at the top form a substantial platform upon which is mounted a large balance (fig. 9). This platform is anchored to the ceiling at four points by tie rods and turn-buckles, shown in fig. 4. The whole apparatus, therefore, is extremely rigid and the balance swings freely.

The top of the chamber is somewhat restricted near the edges (fig. 8) and two lengths of 2-1/2-inch channel support the sides of the opening through which the subject enters at the top (fig. 7).

Both the front and back lower channels upon which the bottom rests are extended so as to provide for supports for the outer walls of asbestos wood, which serve to insulate the calorimeter. Between the channels beneath the calorimeter floor and the 3-inch channels is placed a sheet of zinc which forms the outer bottom metallic wall of the chamber.

In order to prevent conduction of heat through the structural steel all contact between the inner copper wall and the steel is avoided by having strips of asbestos lumber placed between the steel and copper. These are shown as J in fig. 8 and fig. 12. A sheet of asbestos lumber beneath the copper bottom likewise serves this purpose and also serves to give a solid foundation for the floor. The supporting channels are placed near enough together to reinforce fully the sheet of asbestos lumber and enable it to support solidly the weight of the man. The extra strain on the floor due to tilting back a chair and thus throwing all the weight on two points was taken into consideration in planning the asbestos and the reinforcement by the steel channels. The whole forms a very satisfactory flooring.

_Wall construction and insulation._--The inner wall of the chamber consists of copper, preferably tinned on both sides, thus aiding in soldering, and the tinned inner surface makes the chamber somewhat lighter. Extra large sheets are obtained from the mill, thus reducing to a minimum the number of seams for soldering, and seams are made tight only with difficulty. The copper is of standard gage, the so-called 14-ounce copper, weighing 1.1 pounds per square foot or 5.5 kilograms per square meter. It has a thickness of 0.5 millimeter. The whole interior of the skeleton frame of the structural steel is lined with these sheets; fig. 11 shows the copper shell in position.

For the outer metallic wall, zinc, as the less expensive metal, is used. One sheet of this material perforated with holes for the attachment of bolts and other appliances is shown in position on the outside of the wall in fig. 11. The sheet zinc of the floor is obviously put in position before the channels upon which it rests are laid. The zinc is obtained in standard size, and is the so-called 9-ounce zinc, or 0.7 pound to the square foot, or 3.5 kilograms to the square meter. The sheet has a thickness of 0.5 millimeter.

In the cross-section, fig. 7, A represents the copper wall and B the zinc wall. Surrounding this zinc wall and providing air insulation is a series of panels constructed of asbestos lumber, very fire-resisting, rigid, and light. The asbestos lumber used for these outer panels is 6.4 millimeters (0.25 inch) thick. To further aid in heat insulation we have glued to the inner face of the different panels a patented material composed of two layers of sheathing-paper inclosing a half-inch of hair-felt. This material is commonly used in the construction of refrigerators. This is shown as E in fig. 7, while the outer asbestos panels are shown as F.

A detail of the construction of the walls, showing in addition the heating and cooling devices, is given in fig. 12, in which the copper is shown held firmly to the upright channel H by means of the bolt I, screwing into a brass or copper disk K soldered to the copper wall. The bolt I serves the purpose of holding the copper to the upright channel and likewise by means of a washer under the head of the screw holds the zinc to the channel. In order to hold the asbestos-lumber panel A with the hair-felt lining B a threaded rod E is screwed into a tapped hole in the outer part of the upright channel H. A small piece of brass or iron tubing, cut to the proper length, is slipped over this rod and the asbestos lumber held in position by a hexagonal nut with washer on the threaded rod E. In this manner great rigidity of construction is secured, and we have two air-spaces corresponding to the dead air-spaces indicated in fig. 7, the first between the copper and zinc and the second between the zinc and hair-felt.

PREVENTION OF RADIATION.

As can be seen from these drawings the whole construction of the apparatus is more or less of the refrigerator type, _i. e._, there is little opportunity for radiation or conduction of heat. Such a construction could be multiplied a number of times, giving a greater number of insulating walls, and perhaps reducing radiation to the minimum, but for extreme accuracy in calorimetric investigations it is necessary to insure the absence of radiation, and hence we have retained the ingenious device of Rosa, by which an attempt is made arbitrarily to alter the temperature of the zinc wall so that it always follows any fluctuations in the temperature of the copper wall. To this end it is necessary to know _first_ that there is a temperature difference between zinc and copper and, _second_, to have some method for controlling the temperature of the zinc. Leaving for a moment the question of measuring the temperature differences between zinc and copper, we can consider here the methods for controlling the temperature of the zinc wall.

If it is found necessary to warm the zinc wall, a current of electricity is passed through the resistance wire W, fig. 12. This wire is maintained approximately in the middle of the air-space between the zinc wall and hair-felt by winding it around an ordinary porcelain insulator F, held in position by a threaded rod screwed into a brass disk soldered to the zinc wall. A nut on the end of the threaded rod holds the insulator in position. Much difficulty was had in securing a resistance wire that would at the same time furnish reasonably high resistance and would not crystallize or become brittle and would not rust. At present the best results have been obtained by using enameled manganin wire. The wire used is No. 28 American wire-gage and has resistance of approximately 1.54 ohms per foot. The total amount of wire used in any one circuit is equal to a resistance of approximately 92 ohms. This method of warming the air-space leaves very little to be desired. It can be instantaneously applied and can be regulated with the greatest ease and with the greatest degree of refinement.

If, on the other hand, it becomes necessary to cool the air-space next to the zinc and in turn cool the zinc, we must resort to the use of cold water, which is allowed to flow through the pipe C suspended in the air-space between the zinc and hair-felt at approximately the same distance as is the heating wire. The support of these pipes is accomplished by placing them in brass hangers G, soldered to the zinc and provided with an opening in which the pipe rests.